Method and apparatus for controlling the temperature of hot strip



Oct. 3, 1967 R. GRAY 3,344,648

METHOD AND APPARATUS FOR CONTROLLING THE TEMPERATURE OF HOT STRIP Filed Oct. 22, 1964 INVENTOR. Q/Cf/AQDSO/V GRAY ,477ORA/EK United States Patent 3,344,648 METHOD AND APPARATUS FOR CONTROLLING THE TEMPERATURE OF HOT STRIP Richardson Gray, Pittsburgh, Pa., assignor to United Engineering and Foundry Company, Pittsburgh, Pa., a corporation of Pennsylvania Filed Oct. 22, 1964, Ser. No. 405,669 Claims priority, application Great Britain, Nov. 19, 1963, 45,589/ 63 8 Claims. (Cl. 72-364) This invention relates to the rolling of elongated material such as strip produced by a hot rolling mill and, more particularly, to the controlling of the temperature of such material during at least a certain period of the rolling process.

It has been well recognized for many years that in order to obtain the optimum results from the operation of a hot strip mill, close adherence must be given to the regulation of the temperature of the strip. There are two important reasons for controlling the temperature of the strip in such mills: one, for strip metallurgy it is highly advantageous to roll the strip in the finishing train and to coil the strip issuing therefrom within a specified temperature range; and two, for gauge tolerance for the purpose of minimizing the end-to-end temperature differential in the strip during its rolling in the finishing train.

In this connection it must be borne in mind that the operational conditions of the mills may frequently and suddenly change, for example, the unanticipated failure of the strip coiler to receive and coil the strip may result in operational delays, whereby the temperature of the immediately previous strip to be rolled will fall below permissible limits. Such operational delays may have a similar effect on the next several preceding strips to be rolled, since a slowdown or interruption in the operation of the coiler necessitates a reduction of the speed of the finishing train or even in a given case the complete interruption of its operation.

Another varying condition which very frequently changes the thermal characteristic of the strip has reference to the operation of the slab preheating furnaces. During the initial starting-up period of the mill, wherein the furnaces have not reached a uniform heat, the slabs are discharged to the mill at a temperature different from the required temperature whereby, unless this condition is compensated for, the required temperature level and the tolerable end-to-end temperature diflerential are not obtained.

A third variable has reference to the different length slabs rolled by some mills, wherein the temperature characteristics of the strip are such that some adjustment must be made in the mill to obtain and maintain the temperature level and keep the end-to-end temperature differential Within permissible limits.

It is quite customary in continuous and semicontinuous hot strip mills to provide a delay table between the last roughing stand and the first stand of a finishing train. Usually the strip is held on the delay table until the temperature of the strip is reduced to the required level. Once the proper temperature level is obtained, the lead ing end of the strip is advanced into the bite of the first stand of the finishing train, which is operated at a relatively slow speed as compared with the speed of the last stand thereof, and which points up the serious problem relative to the temperature of the strip varying from end to end. As the strip is fed to the first stand of the finishing train, the trailing end thereof is exposed to the atmosphere for a progressively longer period of time than the leading end and, hence, allowed to radiate considerably more than the leading end. Consequently, particularly in recent mill installations where extremely 3,344,648 Patented Oct. 3, 1967 long strips are rolled, a considerable temperature ditferential is created between the two ends of the strip, wherein the trailing end is substantially cooler than the leading end and requires greater rolling pressures to reduce it to a uniform thickness. In the absence of some adjustment of the mill to compensate for this condition, such as an adjustment of the roll pass, the strip will be rolled with a gradual increase in thickness from its leading end to its trailing end.

The present invention relates to a method and apparatus which in one form is adapted to be used in conjunction with the delay table of a finishing train of a hot strip mill and consists of a heat controlling member arranged above the runout table, which can be brought into and out of position either manually or automatically pursuant to the temperature condition of the strip. Should it be desirable to inhibit the radiation of a strip so as to prevent the temperature thereof from falling below the required temperature level, then the member can be placed over the table and above the strip. Should it be desired to employ the member to reduce or eliminate the end-toend temperature differential of the strip, the members can be brought over the leading end of the strip, wherein under certain circumstances it can be heated by the strip itself an amount sutficient so that as the trailing end of the strip passes thereunder, the member being itself heated will inhibit radiation of the strip.

While for the purpose of explaining the invention it will be related to use in conjunction with a delay table of a hot strip mill as indicated above, it will be appreciated that it may be used also to control and maintain the temperature level of the strip passing to the coilers of a hot strip mill.

In one form of the invention there is provided, in conjunction with the delay table of a hot strip mill, a series of heat reflectors arranged above the runout table, which are individually retractable from an operative to an in operative position and wherein there is provided in the Vicinity of the heat reflectors two or more spaced-apart temperature measuring devices, each associated with a reflector, and means controlled by the temperature measuring devices so as to position the reflectors in operative or inoperative positions in accordance with the temperature condition of the strip as determined by the temperature measuring device. Should the first temperature measuring device indicate that the strip temperature is substantially lower than a predetermined temperature, then its associated reflector will be positioned over the strip, thereby reducing the radiation portion of the strip. As the strip passes second or third temperature measuring device indicate that the strip temperature is substantially higher than a predetermined temperature, then its associated reflector will be moved to a position away from the strip, Thus, the reflectors of the present invention can be utilized to maintain the strip temperature level within the required range byinhibiting radiation of the strip, and particularly, if the temperature of the leading end of the strip is high enough, the reflectors can be used to substantially reduce or eliminate the temperature differential between the ends of the strip.

These features and advantages, as well as others, will be more apparent when the following description is read in the light of the accompanying drawing of which:

FIGURE 1 is a schematic view of a portion ofthe hot strip mill illustrating two roughing mill stands, a strip delay table and a finishing train in which connection the present invention has been incorporated;

FIGURE 2 is a schematic elevational view of the delay table showing the heat reflectors shown in FIGURE 1;

FIGURE 3 is a view similar to FIGURE 2, but showing the heat reflectors in their retracted positions; and

of the remaining along, should-the FIGURE 4 is an enlarged elevational view of one of the heat reflectors shown in the previous views.

With reference to FIGURE 1 there is shown, as part of a hot strip rolling mill, two roughing stands 11 and 12, which issue a strip S in the direction of the arrows. Following the roughing stands and in direct line therewith is a strip delay table 13, as shown in FIGURES 2 and 3. The delivery end of the strip delay table communicates with a finishing train consisting of tandernly arranged stands 14, 15, 16, 17, 18 and 19.

Above the delay table 13, as best shown in FIGURES 2 and 3, there are provided three heat reflecting units identified as 22, 23, and 24, each one being connected by means of a pair of overhanging beams arranged at one side of the table and connected to a pair of arms 26, which are in turn pivotally mounted on stands 27 and 28. Each unit is movable in a transverse direction relative to the table by a pair of piston cylinder assemblies 29 which are also connected to one of the arms 26, and pivotally supported by a stand 30. FIGURES 2 and 3 also show rollers 32 that make up the delay table 13, it being understood that the rollers are driven in a customary manner, the details of which are not shown in the drawing.

In referring again to FIGURE 1 it will be noted that between the roughing stand 12 and the heat reflecting unit 22, the heat reflecting units 22 and 23 and between the heat reflector units 23 and 24, three temperature responsive means 33, 34, and 35, respectively, are provided. These means may take the form of pyrometers such as Rayo-Tube temperature detectors made by Leeds & Northrup which may be purchased with potentiometers operated by the pyrometers to produce controlled voltages proportional to the temperature of the strip. As FIGURE 1 shows, the pyrometers 33, 34 and 35 are electrically connected to a temperature regulator 36 which includes three dial setting type rheostats 37, 38 and 39. The temperature regulator will also include three electric on and off type switches, one for each of the pairs of piston cylinder assemblies 29 of the heat reflecting units 22, 23 and 24. In this manner, when the indicated temperature of the strip at any one of the three selected points is higher than the rheostat temperature setting the particular heat reflector will be positioned in the inoperative position, conversely when such temperature is lower than the rheostat setting the particular deflector will be positioned in the operative position. FIGURES 2 and 3 show an elevation of the pyrometer 33 in which it will be noted that it is located so as to be in direct line with a portion of the strip S and that its path of detection is not interfered with by the reflector when the latter is in its operative position.

FIGURE 4 illustrates an end view of one form of the heat reflecting unit which, as shown, is made up of similarly formed fabricated thin plates 41 and 42, each corrugated as illustrated with respect to plate 42 and arranged at right angles to each other, thereby giving the required structural stiflness. The thinness of the plates will permit the plates to be heated very quickly to a luminous temperature thereby greatly increasing their usefulness in inhibiting the radiation of the strip. This luminous temperature can be maintained by employing sufficient insulation on the top surfaces on each plate 41 and 42 thereby substantially preventing heat losses. In this way the leading end of the strip can be employed to heat up the reflectors, which heated reflectors can then be used to greatly inhibit the radiation of the trailing end of the strip.

Assuming in a given case, that 60% of the strip is available to heat the reflector plates 41 and 42, the following will serve to illustrate the effectiveness of the reflectors in inhibiting radiation in a given case.

Assuming still further that the reflector plate 42 is 16 ga. type 310 stainless steel, then we have:

Specific heat=0.l2 B.t.u./of x lb. (from Allegheny- Ludlum certified data).

4 Emissivity ratio=0.8 (Marks 5 ed., p. 382) (ratio of gray body to black body radiation). Unit weight=2.5 lb./ft. Room temp.=70 F. Temp. for inhibiting radiation (assumed)=1570 F. Entry strip speed at stand 14 (assumed)=200 f.p.m.

Now in computing the temperature losses of the trailing end of the strip due to radiation and in referring to the Stefan-Boltzmann law, using Emissivity Ratio for gray body conditions, we have the following equation:

4 [(IEI) m) 1 wherein:

0 :0.173 (Stefan-Boltzmann constant) black body. T =Radiating average temp. R.

T =Absorbing average temp. R.

R.=Absolute temp. of radiating surface.

To find the length of strip required to heat the reflector from 70 to 1570 we have:

Length (ft.)

Rate of heat transfer Heat Transferred per sq. ft. Sp. ht. X AT Xunit weight Rate of heat transfer (Stefan-Boltzmann) B.t.u.

A00 sq. ft. XhOur) Since 157 ft. is to he only 60% of the total strip length, the total length of the strip will equal 262 ft. Thus it is seen that for the above-assumed conditions the strip velocity and strip length are the only variables in the immediate above equation, so that the ratio can be written:

Strip length 262 ft. ft. Strip velocity 200 f.p.m. f.p.m.

A complete description of one operation of the illustrated embodiment of the invention will now be given: Assuming that the reflectors 22, 23 and 24 are in their operative positions as a strip is delivered from the roughing stands 11 and 12, it will proceed down the delay table 13 and pass under the pyrometer 33. Should the pyrometer indicate that the temperature level is below the required level, as set by the rheostat 37 of temperature regulator 36, the piston cylinder assemblies 29 of the reflector 22 will be automatically operated to position the reflector over the strip, i.e., into the position illustrated in FIGURE 2. The thin gauge plate 42 of the heat reflecting unit will be quickly heated to a glowing temperature by the strip and thereafter further radiation of the strip will be substantially inhibited.

As the leading end of the strip advances over the delay table 13 and passes under the pyrometer 34, should the strip temperature as detected by the pyrometer 34 be significantly below the setting of the rheostat 38 of the temperature regulator 36, then the reflector 23 will be moved to the operative position by operation of their piston cylinder assemblies 29.

Should the detected temperature of the strip by the pyrometer 35 be higher than the setting of the rheostat 39, then the piston cylinder assemblies 29 of the reflector 24 will be automatically moved to its inoperative position. Thus it will be appreciated that the automatic control of the reflectors 22, 23 and 24 can be employed to both control the temperature level and reduce the temperature differential between the ends of the strip.

It will be appreciated that, while in the illustration only three reflectors have been employed, for a given case several reflectors can be employed which may operate independently or in series with adjacent reflecting units, and that the reflectors may include auxiliary heating means.

In accordance with the provisions of the patent statutes, I have explained the principle and operation of my invention and have illustrated and described what I consider to represent the best embodiment thereof. However, I desire to have it understood that Within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. In a method of controlling the radiation losses of a heated strip during a rolling process, the steps comprising:

passing the strip over a predetermined path of travel during a rolling process,

selectively positioning a radiation inhibiting member between a position over the strip and a position ,away from said strip to control the radiation losses, thereby to obtain a desired temperature for at lea-st a portion of the strip.

2. In a method of controlling the radiation losses of a heated strip during a rolling process, the steps comprising:

passing the strip over a predetermined path of travel during a rolling process,

determining the temperature of the strip during the rolling process and comparing the determined temperature with a desired temperature, and should the determined temperature be below the desired temperature, positioning a radiation inhibiting member over the strip.

3. In a method, according to claim 1, in which there is provided at least two radiation inhibiting members, the additional steps of:

determining the temperature of the strip at least at said two members before the strip passes under said two members, and independently positioning the members over the strip pursuant to the determined temperature thereof in .3 order to control the radiation losses longitudinally of the strip.

4. In a method, according to claim 1, including the additional steps of:

heating the member by the leading end of said strip,

and

thereafter maintaining the member over the strip in its heated condition to inhibit the radiation losses of a succeeding portion of the strip. 5. In an apparatus for controlling the radiation losses of a heated strip during a rolling process, comprising:

a delivery table arranged in front of a rolling mill on which a strip is held prior to entrance into the mill,

a plurality of heat-deflecting shields arranged longitudinally of the path of the strip and above said delivery table, and

means for moving at least one of said shield-s from a position over the strip where it inhibits radiation thereof to a position on one side of the table in which position radiation by said one shield is uninhibited.

6. An apparatus according to claim 5 wherein said shields comprise a first corrugated thin metallic sheet having its corrugations extending in a first direction and a second corrugated thin metallic sheet having its corrugations extending in a direction perpendicular to the corrugations of said first sheet.

7. An apparatus, according to claim 5, including means for producing a signal representative of a desired temperature level of the strip,

means for producing a second signal representative of the actual temperature of a portion of the strip,

means for determining any difference between said two signals, control means operable by determining means when the temperature of the strip difiers from said desired temperature for moving one or more of said shields over the strip to inhibit radiation losses thereof.

8. In an apparatus, according to claim 5, in which the temperature of the strip tends to gradually decrease from the leading end to the trailing end thereof,

means for producing a signal representative of the temperature of a preceding portion of the strip, means for producing a second signal representative of a desired end-to-end temperature of the strip, means for determining any differences between the said two signals, and

control means operable by said determining means when the temperature of the strip differs from said desired temperature for controlling the position of said shields and thereby the radiation losses of the strip to obtain a substantial uniform end-to-end temperature of the strip.

References Cited UNITED STATES PATENTS 1,676,176 7/1928 Biggol't r 72202 1,718,806 6/1929 Witting 7213 FRANCIS S. HUSAR, Primary Examiner. 

1. IN A METHOD OF CONTROLLING THE RADIATION LOSSES OF A HEATED STRIP DURING A ROLLING PROCESS, THE STEPS COMPRISING: PASSING THE STRIP OVER A PREDETERMINED PATH OF TRAVEL DURING A ROLLING PROCESS, SELECTIVELY POSITIONING A RADIATION INHIBITING MEMBER BETWEEN A POSITION OVER TH STRIP AND A POSITION AWAY FROM SAID STRIP TO CONTROL THE RADIATION LOSSES, THEREBY TO OBTAIN A DESIRED TEMPERATURE FOR AT LEAST A PORTION OF THE STRIP. 